Impellers are widely used to move fluids and/or extract energy from them. Example applications include aircraft and water craft propulsion systems, power generation, turbocharging, gas compression, air separation and refrigeration.
Impellers may be classified as open, where the impeller blades rotate next to a fixed conduit surface, or enclosed (or “shrouded”), where an enclosing shroud is affixed to the blades and rotates with the impeller. Fluid flowing through the internal passages of a shrouded impeller interacts less with stationary conduit walls than in an open impeller. The relative velocity between the shrouded impeller and the contained fluid at any given radius may be small compared to an open impeller, resulting in less frictional phenomena, such as wear or pressure loss.
A shrouded impeller may be an integral, or one-piece unit, manufactured from one solid piece of material or it may instead be constructed from two or more components, which are attached together to form the finished product. In the latter case, the separate parts most commonly include a bladed hub and a separate shroud. The main advantage of a one-piece shrouded impeller is that it lacks seams where multiple pieces would otherwise be attached. Such seams initiate cracking, and may also interfere with the flow of fluid through the impeller. However, manufacturing a one-piece impeller may be more expensive and time consuming than manufacturing and assembling an impeller from multiple components. Manufacturing and assembling a shrouded impeller from two or more pieces may allow the use of shorter tools. Shorter tools may suffer less wear than longer reach tools, since they experience less deflection and vibration while machining and cutting, resulting in better dimensional accuracy and surface finish.
There is therefore an unaddressed need in the industry for a process of manufacturing shrouded impellers in two or more pieces that approach the strength and performance of a one-piece shrouded impeller.